The present invention relates to data currency improvement and, more specifically, to a method of data currency improvement for cross-site queries when using asynchronous data mirroring technologies.
A number of information technology (IT) installations are replicating data to multiple sites that may be remote from each other. This is done for a number of reasons, including, but not limited to, maintaining current or near-current data at a secondary site so that recovery from unscheduled site outages can be done more quickly. As the distance between sites increases, however, the use of synchronous data replication technologies becomes impractical because the replication delays result in long transaction times that are unacceptable. Therefore, at greater distances asynchronous replication technologies are usually deployed.
The creation of a secondary site is often expensive and represents a duplication of all the hardware and software needed to support a number of applications with respect to a primary site. Furthermore, restricting all read and update activity to a single site burdens the originating site with the preponderance of the workload while the secondary site or sites are often lightly-loaded. To counteract this, an enterprise can choose to allow read activity from all sites while restricting write activity to a single site, or even to allow unrestricted multi-site read/write activity.
Because there is an inherent replication delay involved in transmitting data from one site to another, it is possible for a write transaction to be processed at one site and a subsequent query (read) transaction to be processed at another site before the replication occurs. When this happens, the query transaction data is outdated.